Many air conditioners include economizer cycles to reduce energy use when the outside air is cool and dry enough to provide required system cooling. During an economizer cycle, an air conditioner's mechanical refrigeration equipment is turned off, cool outside air is introduced into the enclosure served by the air conditioner, and warmer inside air is exhausted from the enclosure. An economizer cycle uses significantly less energy than a refrigeration cycle because it only requires operation of a relatively low power blower.
Air conditioners typically switch between their economizer cycles and conventional refrigeration cycles by measuring an outdoor dry bulb (DB) temperature, comparing the DB temperature to a target temperature, and switching to an economizer cycle if the outdoor air temperature is below the target. For example, many air conditioners trigger their economizer cycles when outdoor temperatures are at or below a supply air temperature setpoint, which is typically within the range of 55°-59° F.
Another method to switch between refrigeration and economizer cycles senses outdoor and return air enthalpy and switches to the economizer cycle whenever the outdoor air enthalpy is less than that of the return air.